1. Field of the Invention
The present invention relates to a vibration gyro sensor for detecting an angular velocity of an object, a control circuit therefor, and an electronic apparatus mounted with the vibration gyro sensor.
2. Description of the Related Art
Up to now, so-called vibration gyro sensors have been widely used as angular velocity sensors for consumer use. The vibration gyro sensors are sensors that detect angular velocities by allowing a cantilever vibrator to vibrate at a predetermined resonance frequency and detecting Coriolis force generated due to an influence of the angular velocity by a piezoelectric element or the like.
The vibration gyro sensors have advantages in that the sensors have a simple mechanism, requires short time to activate, and can be manufactured at low costs. The vibration gyro sensors are mounted to, for example, electronic apparatuses such as a video camera, a virtual reality apparatus, and a car navigation system, and are used as sensors in shake detection, movement detection, and direction detection, respectively.
In recent years, the vibration gyro sensors are required to be downsized and improved in performance due to the downsizing and improvement in performance of the electronic apparatuses to which the vibration gyro sensors are mounted. For example, because of multi-functionalization of the electronic apparatuses, demands are made to mount the vibration gyro sensor to a substrate in combination with various sensors for other purposes, thereby reducing a size thereof. A generally-used technique for realizing such reduction in size is called MEMS (Micro Electro Mechanical System) which involves using an Si substrate and forming a structural body using a thin-film process and a photolithography technique used in forming semiconductors.
Incidentally, a vibration system becomes light along with the downsizing of the vibration gyro sensor. However, because the Coriolis force is proportional to the weight of the vibration system, detection sensitivity deteriorates that much. Further, because an amplitude of the vibrator becomes small when a power supply voltage is decreased due to the downsizing of the vibration gyro sensor, the detection sensitivity also deteriorates thereby. An S/N of a detection output signal is degraded by the deterioration of the detection sensitivity.
Thus, to solve the problems as described above, there is disclosed a technique in which drive signals having the same phase and amplitude and output from two detection electrodes are added in an addition circuit and the signal whose phase has been inverted in an inversion circuit is input to the two detection electrodes (see, for example, Japanese Patent Application Laid-open No. 2000-205861 (paragraphs (0005) and (0016), and FIG. 1)).